The present invention relates generally to a signal transmission system implemented with optical fibers and related optical components. More particularly, this invention relates to an optical interleave device implemented in a dense wavelength division multiplexing (DWDM) system.
As the optical wavelength division multiplexing (WDM) technology gradually becomes the standard backbone network for the fiber optic communication systems, a challenge is continuously faced by those of ordinary skill in the art to increase the transmission capacity due to the bandwidth limitations of the optical fiber signal transmission systems. Specifically, the bandwidth of the optical fiber amplifier, such as Erbium doped fiber amplifier (EDFA), is limited as more and more channels are inserted into the transmission band. The wavelength spacing between adjacent channels employed for carrying the optical signals becomes narrower when more channels are xe2x80x9csqueezed inxe2x80x9d the transmission band for the purpose of satisfying a requirement of increasing the transmitting capacity of the signal transmission system. However, the wavelength division multiplexing (WDM) technologies employing dielectric filters are confronted with a limitation due to the ability to separate one channel from adjacent ones when the channel spacing is further reduced with increased number of channels. Another technical approach applies a fiber grating technology for multiplexing and de-multiplexing the optical signals transmitted over optical fiber systems. However, the fiber grating technology is limited by the temperature sensitivity problems when the channel spacing becomes narrower.
As the fiber optical industry is now providing stable products for 200 GHz and 100 GHz channel spacing WDM signal transmission over the optical fiber systems, a new interleave technology emerges in attempt to further reduce the channel spacing to achieve higher bandwidth. An interleaver is an optical device employed to select wavelength channel according to predefined channel spacing. As an example, when optical signals of N channels with 50 GHz channel spacing are transmitted to an optical interleaver, the optical interleaver separates the optical signals into a first group of signals consisted of channels 1, 3, 5, . . . Nxe2x88x921, and a second group of signals consisted of channels of 2, 4, 6, . . . N, with channel spacing of 100 GHz. Therefore, fiber optical system implemented with an optical interleaver is capable to process optical signals transmitted with a narrow channel spacing by first separating the signals into groups of signals with broader channel spacing such that optical devices currently provided by the optical fiber industry can be applied to further process these optical signals outputted from the interleaver.
As the WDM technology now enables the utilization of substantially wider fiber bandwidth for signal transmission, a number of prior art patents disclosed methods and configurations deal with interleaver. The interleaver according to the state of the art are bulky, and having a high production cost due to the need of using more expensive materials and optical elements.
Therefore, a need still exists in the art of manufacturing and designing the fiber optic interleaver to provide simpler configurations that would reduce size and production cost.
It is therefore an object of the present invention to provide a new design and configuration for manufacturing and assembling a fiber optic interleaver with reduced size to provide compact interleaver with lower the production.
Specifically, it is an object of the present invention to provide an interleaver implemented with new configuration by employing a phase delay generating means such as a glass plate to construct a type of Mach-Zender interferometer to induce an optical interference for enhancing signal transmission at certain wavelengths. The phase delay generating means such as a glass plate are positioned between a pair of collimator lenses for inducing interference between two portions of collimated beam transmitted with different phases. Lights with certain wavelength are transmitted and lights with other wavelengths are suppressed. Therefore, the phase delay generating means can be implemented to selectively enhance and suppress signal transmission with predefined wavelengths thus achieving the function as an interleaver.
Briefly, in a preferred embodiment, the present invention includes an optical interleaver that includes a first collimator lens for collimating an input optical signal into collimated beams and a second collimator lens for focusing the collimated beam into an output optical fiber. The interleaver further includes a phase delay generating means for generating a phase-delay between portions of the collimated beam for generating interference in the second collimator lens for selectively enhance signal transmission of certain wavelengths. In a preferred embodiment, the phase delay generating means comprising a glass plate blocking a portion of the collimated beam for generating a phase delay for a portion of the collimated beam passing through. In another preferred embodiment, the phase delay generating means comprising a glass plate having an upper portion covering an upper portion of the collimated beam. The glass plate having a lower portion covering a lower portion of the collimated beam for generating a phase delay between the upper portion and lower portion of the collimated beam. In another preferred embodiment, the interleaver further includes a control means for controlling the phase delay generating means for selectively generating signal transmission at different wavelengths according to the interference generated in the second collimator lens. In yet another preferred embodiment, the phase delay generating means comprising a glass plate having a plurality of predefined segments. Each segment has different combination of plate-thickness and diffraction index wherein the phase delay generating means is controlled by the control means for selectively generating signal transmission at different wavelengths with a predefined program. In another preferred embodiment, the phase delay generating means comprising a set of cascaded interferometer for making top flat profile of the transmissions band. In another preferred embodiment, each of the a set of cascaded interferometer comprising a phase delay plate and a half-pitch GRIN lens. In another preferred embodiment, each of the a set of cascaded interferometer comprising a phase delay plate and a pair of focus and collimating lenses. In another preferred embodiment, the interleaver further includes a reflective means for reflecting a portion of the collimated beam as second beam transmitted along a second optical path away from the collimated beam. The interleaver further includes a third collimator lens for focusing the second group of beam into a second output optical fiber. And, the interleaver further includes a second phase delay generating means for generating a second phase-delay between portions of the second beam. Thus an interference in the third collimator lens is generated for selectively enhance signal transmission of a second set of wavelengths outputting from the second optical fiber.
In summary, this invention discloses an optical interleaver that includes a phase delay generating means for generating a phase delay between different portions of optical beam for selectively enhancing signal transmissions at certain wavelengths resulting from interference between the different portions of optical beam. In a preferred embodiment, the interleaver further includes a control means for controlling the phase delay generating means controlling a selection of certain wavelengths for enhanced signal transmission. In another preferred embodiment, the phase delay generating means further comprising an optical element for transmitting optical beam through. In another preferred embodiment, the phase difference generating means further comprising the optical element for transmitting optical beam through with at least two portions of different thickness. In another preferred embodiment, the phase delay generating means further comprising the optical element for transmitting optical beams through with at least two portions of different diffraction indexes.